The contact material of vacuum interrupters is required to satisfy characteristics, such as (1) the breaking capacity being large, (2) the withstand voltage capability being high, (3) the contact resistance being low, (4) the deposition resistance property being high, (5) the contact consumption being low, (6) the chopped current being low, (7) the workability being excellent, and (8) the mechanical strength being high.
Since some of these characteristics conflict with each other, there is no contact material satisfying all of the above characteristics. Cu—Cr electrode materials have characteristics, such as the breaking capacity being large, the withstand voltage capability being high, and the deposition resistance property being high. Therefore, they are widely used as contact materials of vacuum interrupters. Furthermore, there is a report that, in Cu—Cr electrode materials, one having a finer particle size of Cr particles is superior in breaking current and contact resistance (for example, Non-patent Publication 1).
In recent years, there has been progress in making vacuum interrupters conducting are extinction of vacuum circuit breakers have smaller sizes and larger capacities. Thus, there has been an increasing demand for Cu—Cr based contact materials having withstand voltage capabilities superior to those of conventional ones, which are essential for making vacuum interrupters have smaller sizes.
For example, in Patent Publication 1, there is described a method for manufacturing an electrode material, in which, as a Cu—Cr based electrode material excellent in electrical characteristics such as current breaking capability and withstand voltage capability, respective powders of Cu used as a base material, Cr for improving electrical characteristics, and a heat-resistant element (Mo, W, Nb, Ta, V, Zr) for making the Cr particles finer are mixed together, and then the mixed powder is put into a mold, followed by pressure forming and making a sintered body. Specifically, a heat-resistant element, such as Mo, W, Nb, Ta, V or Zr, is added to a Cu—Cr based electrode material containing as a raw material a Cr having a particle size of 200-300 μm, and the Cr is made fine through a fine texture technology, an alloying process of the Cr element and the heat-resistant element is accelerated, the precipitation of fine Cr—X (Cr making a solid solution with the heat-resistant element) particles in the inside of the Cu base material texture is increased, and the Cr particles having a diameter of 20-60 μm in a configuration to have the heat-resistant element in its inside are uniformly dispersed in the Cu base material texture.
Furthermore, in Patent Publication 2, without going through the fine texture technology, a powder obtained by pulverizing a single solid solution that is a reaction product of a heat-resistant element is mixed with a Cu powder, followed by pressure forming and then sintering to manufacture an electrode material containing Cr and the heat-resistant element in the electrode texture.
By forming an arc-resistant metal's fine dispersion texture as described in Patent Publication 2, withstand voltage capability and breaking capability are improved, but deposition resistance capability becomes worse to result in a deposition between the electrodes when applying a large current in a closed condition of the electrodes. This lowering of deposition resistance capability causes vacuum circuit breakers to have larger sizes, and this has been a task for mass-production.
Thus, we tried to manufacture an electrode material having superior withstand voltage capability and deposition resistance capability by adding a low melting metal (e.g., Te, etc.) to an electrode material having a MoCr fine dispersion texture.
However, in the sintering step of a MoCr fine dispersion electrode material containing a low melting metal added thereto, there was a risk that vacancies were generated in the electrode interior to result in lowering of packing percentage of the electrode material. Furthermore, there was a risk that dispersion occurred in packing percentage by the temperature distribution of the sintering furnace. If packing percentage of the electrode material lowers by the generation of vacancies in the electrode material, there is a risk that brazing material (e.g., Ag) is absorbed into vacancies of the electrode's inside in the brazing step to result in difficulty in brazing of the electrode material.